A magnetic sensor for detecting a physical quantity can detect motion such as movement, rotation, etc. of a detection object constructed by a magnetic substance in non-contact. Accordingly, for example, the magnetic sensor is used in a throttle valve aperture sensor, etc. of a vehicle mounting internal combustion engine as an angle detecting sensor. In particular, the magnetic sensor constructed by arranging a Hall element as an element for utilizing the Hall effect can also distinguish a magnetic pole. Therefore, this magnetic sensor is also widely utilized in a magnetic pole sensor, etc. of a brushless motor. First, a magnetic field detection principle of this Hall element will be explained with reference to FIG. 16.
When a magnetic field perpendicular to a carrier moved within a semiconductor is applied, electromotive force is generated within the semiconductor in a direction perpendicular to both the carrier and the magnetic field by Lorentz force. This electromotive force is called a Hall voltage. Concretely, as shown in FIG. 16, for example, in the Hall element 100 of width W, length L and thickness d, when a driving electric current I is flowed from terminal TI1 to terminal TI2 and the magnetic field of magnetic flux density B is applied to this Hall element 100, Hall voltage Vh shown by the following relation formula:Vh=(Rh×I×B/d)×cos θ
is generated between terminal V1 and terminal V2. Here, angle θ is an angle formed between the Hall element 100 and a direction of the magnetic field. Further, Rh is a Hall coefficient, and is a value shown by the relation formula of Rh=1/(q×n) when an electric charge is q and a carrier density is n.
Thus, the Hall voltage Vh generated in the Hall element becomes a function of magnetic flux density B and angle θ. Therefore, the strength of the applied magnetic field and the direction (angle θ) of the magnetic field can be detected in accordance with the magnitude of this Hall voltage Vh.
A lateral Hall element described in e.g., “Integrated three-dimensional magnetic sensor” published in Electricity Society thesis journal C, Vol. 109, No. 7, pp. 483-490 in 1989 is known as a general Hall element. This lateral Hall element detects a magnetic field component perpendicular to the surface of a substrate (i.e., wafer). Here, the structure and magnetic field detecting principle of this lateral Hall element will be explained. FIG. 17A typically shows a planar structure of this lateral Hall element. FIG. 17B typically shows a sectional structure of this lateral Hall element along XVIIB-XVIIB within FIG. 17A.
As shown in FIGS. 17A and 17B, this lateral Hall element is constructed by arranging a semiconductor support layer (P-sub) 110 constructed by e.g., silicon of P-type, and a semiconductor layer (N-well) 111 of N-type formed through ion implantation to a surface portion of this semiconductor support layer 110. On the surface of the semiconductor layer 111, electrode a and electrode b for supplying a driving electric current, and electrode c and electrode d for detecting the Hall voltage are arranged at four corners in a mode opposed to each other. Further, on the surface of the semiconductor layer 111, N-type diffusion layers 112a to 112d constructed by N-type higher in concentration than this semiconductor layer 111 are formed to form ohmic contact with these electrodes a to d.
Here, for example, when a driving electric current I is supplied between electrode a and electrode b, this driving electric current I is flowed in a horizontal direction with respect to the surface of the semiconductor layer 111. In a state in which the driving electric current I is flowed in this way, as shown by arrows in FIGS. 17A and 17B, when a magnetic field (magnetic flux density B) including a component perpendicular to the surface of the semiconductor layer 111 is applied, the above Hall voltage Vh is generated between electrode c and electrode d. The magnetic field component perpendicular to the surface of the semiconductor layer 111 can be detected by detecting this Hall voltage Vh.
Further, in recent years, a Hall element for detecting a horizontal magnetic field component with respect to the substrate (wafer) surface is also proposed. A Hall element similarly described in e.g., “Integrated three-dimensional magnetic sensor” published in Electricity Society thesis journal C, Vol. 109, No. 7, pp. 483-490 in 1989, and “Characteristic and high sensitivity formation of vertical Hall element” published in Electricity Society thesis journal E, Vol. 117, No. 7, pp. 364-370 in 1997, a so-called vertical Hall element is known as such a Hall element. Next, the structure and magnetic field detecting principle of this vertical Hall element will be schematically explained with reference to FIGS. 18 and 19. FIG. 18 typically shows a planar structure of this vertical Hall element. FIG. 19 typically shows a sectional structure of this vertical Hall element along XIX-XIX within FIG. 18.
As show in FIG. 19 illustrating this sectional structure, this vertical Hall element is constructed by arranging a semiconductor support layer (P-sub) 120 constructed by e.g., silicon of P-type, an N-type (N+) embedded layer BL buried and formed on the surface of this semiconductor support layer 120, and a semiconductor layer 121 of N-type formed on this N-type embedded layer BL by epitaxial growth. Impurity concentration of the above N-type embedded layer BL formed on the surface of the semiconductor support layer 120 is set to concentration higher than that of the above semiconductor layer 121.
In the semiconductor layer 121, a diffusion layer 122 of P-type is formed in a square sleeve shape so as to be connected to the above semiconductor support layer 120. On an inner circumferential face of this diffusion layer 122, diffusion layers 123, 124 of the same P-type are formed so as to be connected to the above N-type embedded layer BL. The semiconductor layer 121 is divided into three areas 125a to 125c approximately formed in a rectangular parallelepiped shape by diffusion layers 122 to 124. On the surface of the area 125a located at the center among these areas 125a to 125c, three diffusion layers 126a, 126d, 126e of N-type (N+) are formed on a straight line with the diffusion layer 126a as a center. On the other hand, a diffusion layer 126b of N-type (N+) is formed at the surface center of the area 125b, and a diffusion layer 126c of the same N-type (N+) is formed at the surface center of the area 125c. Namely, as shown in FIG. 19, the above diffusion layer 126a is arranged so as to be opposed to each of the diffusion layer 126b and the diffusion layer 126c through the above diffusion layer 123 and the above diffusion layer 124. The above diffusion layers 126a to 126e function as a contact area, and are respectively electrically connected to terminal S, terminal G1 terminal G2, terminal V1 and terminal V2. In this vertical Hall element, as shown by a broken line within FIG. 18, an area nipped by the above diffusion layer 126d and diffusion layer 126e in an area electrically partitioned within the substrate of the above area 125a becomes a so-called Hall plate HP.
Here, for example, when a constant driving electric current is flowed from terminal S to terminal G1 and is also flowed from terminal S to terminal G2, this driving electric current is respectively flowed from the diffusion layer 126a of the surface of the semiconductor layer 121 into the diffusion layer 126b and the diffusion layer 126c through the above Hall plate HP and the N-type embedded layer BL. Namely, the driving electric current mainly including a component perpendicular to the substrate surface is flowed to the above Hall plate HP. Thus, in a flowing state of the driving electric current, as shown by arrows within FIGS. 18 and 19, when a magnetic field (magnetic flux density B) including a component parallel to the surface of the semiconductor layer 121 is applied, the above Hall voltage Vh is generated between terminal V1 and terminal V2. A magnetic field component parallel to the surface of the semiconductor layer 121 can be detected by detecting this Hall voltage Vh.
In such a vertical Hall element, in addition to this, there is also an element having a structure able to be manufactured through a CMOS process. In accordance with the vertical Hall element able to be manufactured through this CMOS process, manufacture cost is reduced in comparison with the vertical Hall element manufactured through a bipolar process, and high integration is easily performed. Accordingly, various correction circuits of high precision can be mounted onto the same chip. Next, the vertical Hall element of this kind will be schematically explained with reference to FIGS. 20 and 21. FIG. 20 typically shows a planar structure of this vertical Hall element. FIG. 21 typically shows a sectional structure of the same vertical Hall element along XXI-XXI within FIG. 20.
As shown in FIG. 21, this vertical Hall element is constructed by arranging a semiconductor support layer (P-sub) 130 constructed by e.g., silicon of P-type, and a semiconductor area (Nwell) 131 of N-type formed as a diffusion layer (well) by introducing e.g., electric conductivity type impurities of N-type on the surface of the semiconductor support layer 130. Further, as shown in FIG. 20 illustrating its planar structure, in this semiconductor support layer 130, a diffusion layer (Pwell) 132 of P-type is formed as a diffusion separating wall so as to surround the above semiconductor area 131. Diffusion layers (Pwell) 133, 134 of P-type having a diffusion depth shallower than that of the above semiconductor area 131 are formed on an inner circumferential face of this diffusion layer 132. The surface vicinity of the semiconductor area 131 is divided into three areas 135a to 135c approximately formed in a rectangular parallelepiped shape by these diffusion layers 132 to 134. In this vertical Hall element, on the surface of the area 135a located at the center, three diffusion layers 136a, 136d, 136e of N-type (N+) are also formed on a straight line with the diffusion layer 136a as a center. On the other hand, a diffusion layer 136b of N-type (N+) is formed at the surface center of the area 135b, and a diffusion layer 136c of N-type (N+) is formed at the surface center of the area 135c. In this vertical Hall element, as shown by a broken line within FIG. 20, an area nipped by the above diffusion layer 136d and the above diffusion layer 136e in an area electrically partitioned in the substrate interior of the above area 135a becomes a Hall plate HP.
In the vertical Hall element having such a structure, when a constant driving electric current is flowed from terminal S to terminal G1 and is also flowed from terminal S to terminal G2, the driving electric current mainly including a component perpendicular to the surface of the semiconductor area 131 is also flowed to the above Hall plate HP. Therefore, a magnetic field component parallel to the surface of the above semiconductor area 131 can be also detected by the vertical Hall element of such a structure through the detection of the Hall voltage Vh.
Here, as shown in FIG. 22A, two magnets MG1, MG2 formed in a curved shape are fixed to a rotating body. A Hall element 140 is arranged at the center within an area nipped by the N-pole of the magnet MG1 and the S-pole of the magnet MG2. A detecting mode of a rotation angle will be explained when the magnetic field of a direction shown by an arrow within this figure is applied to the Hall element 140. In such a construction, when only the rotating body fixing the two magnets MG1, MG2 thereto is rotated, as shown in the upper view of FIG. 22B, the Hall voltage Vh changed in a sine wave shape in accordance with the rotation angle of the rotating body is outputted from the Hall element 140. This Hall voltage Vh and the rotation angle theoretically have one-to-one corresponding relation. Therefore, the rotation angle of the rotating body can be calculated on the basis of the above Hall voltage Vh outputted from the Hall element 140. However, in the real use, as shown by the lower view of FIG. 22B, only a voltage value within an area AR for linearly changing the Hall voltage Vh with respect to the transition of the rotation angle among the Hall voltage Vh thus obtained is used in the detection of the rotation angle to reduce arithmetic load applied in the detection of the rotation angle and improve detection accuracy, etc.
On the other hand, as shown as a line segment R in FIG. 22C, the Hall voltage Vh actually detected is separated from a line segment T showing the above theoretical Hall voltage Vh by various error factors in the real situation. The following two factors are mainly considered as this factor.
The existence of an offset voltage is enumerated as a first factor. The offset voltage is a voltage applied when no magnetic field is applied (magnetic flux density B=0). When no magnetic field is applied to the Hall element, it is ideal that the offset voltage becomes “zero”. However, in reality, even when no magnetic field is applied to the Hall element, a voltage (offset voltage) for entirely raising the Hall voltage Vh is generated. Therefore, as shown by a one-dotted chain line within FIG. 22C, an output voltage from the Hall element is entirely raised by the offset voltage in comparison with the original Hall voltage Vh. There are the following matters as a generating factor of such an offset voltage.
The offset voltage is generated by an alignment shift when the Hall element is manufactured. In the previous FIG. 18, when a shift is caused in alignment of diffusion layers 122 to 124 and diffusion layers 126a to 126e and the relative position relation of diffusion layers 122 to 124 and diffusion layers 126a to 126e is shifted, an offset is caused in the flow of the driving electric current from terminal S to terminal G1 and terminal G2. An equipotential line within the Hall element is deformed by this offset of the driving electric current. Therefore, the offset voltage is generated between electrode c and electrode d.
The offset voltage is also generated by external mechanical stress. A package (an adhesive of mold, silver paste, etc.) for sealing the Hall element is enumerated as a factor of the mechanical stress generation. When the external mechanical stress is applied to the Hall element, a resistance value within the Hall element is changed by a piezo resistance effect. Such mechanical stress is not uniformly applied to the Hall element. Therefore, an unbalance is generated with respect to the resistance value within the Hall element. This unbalance of the resistance value within the Hall element appears as the offset voltage.
Temperature characteristics of the magnet for applying the magnetic field to the Hall element and temperature characteristics of the Hall element itself are enumerated as a second factor.
A voltage as shown by a two-dotted chain line within FIG. 22C is finally outputted from the Hall element by these factors.
A change of the Hall voltage Vh generated by the existence of such an offset voltage and the temperature characteristics is generally corrected by using a correction circuit. In this change, the above change due to the offset voltage is generated by a mechanical factor of the structure of the Hall element, etc. Therefore, there are many cases in which it is sufficient to make a correction by only once through the correction circuit. Accordingly, it is not seen as a problem so much in the angular detection using the Hall element. On the other hand, with respect to the above change caused by temperature characteristic, the correction every each temperature is required so that its correction is complicated and cannot be also neglected from a viewpoint of improvement of detection accuracy of the Hall element
More particularly, temperature characteristics of the magnet for applying the magnetic field to the above Hall element and temperature characteristics of the Hall element itself, i.e., the relation of the Hall voltage Vh and temperature is generally represented by a secondary function. Therefore, it is necessary to increase the number of times of the correction of the Hall voltage Vh made every temperature and make a curve correction in the secondary function to detect the magnetic field of high precision by correcting the change of the Hall voltage Vh using such temperature characteristics. However, if the number of times of the correction is increased, time until the calculation of the magnitude of the magnetic field applied to the same Hall element from the Hall voltage is increased. Further, if the curve correction is made, a circuit scale is increased and an increase of a chip size is caused. Therefore, in each case, non-efficiency is caused.
In particular, in the above vertical Hall element, as shown below, a spreading method of a depletion layer is different in accordance with temperature. Therefore, a bending degree of a curve showing the relation of temperature and the Hall voltage in the above temperature characteristic tends to be more emphasized, and the correction of the Hall voltage caused by the temperature characteristic is more complicated. Further, the width of the depletion layer is also dispersed by dispersion of the diffusion layer in manufacture. Therefore, dispersion of the Hall voltage every individual also becomes large.
Namely, in the vertical Hall element, as shown by a broken line in FIG. 23, when the driving electric current is flowed to the same element, depletion layers are respectively generated in a PN junction portion between the semiconductor area 131 and diffusion layers 133, 134 and a PN junction portion between the semiconductor area 131 and the diffusion layer 132. The sizes of these depletion layers are also changed in accordance with temperature. Further, in the vertical Hall element, diffusion concentration of the diffusion layer is thin. Therefore, the above depletion layer is more easily spread in two directions (horizontal direction in this figure) with respect to the direction of the electric current, and the shape of the Hall plate HP is easily distorted. As shown in FIG. 24, temperature dependence more notably appears in the vertical Hall element from such reasons. It becomes difficult to precisely correct the change of the Hall voltage caused by the temperature characteristic.
Accordingly, a sensor able to correct the change of the output voltage caused by the temperature characteristic on the basis of high accuracy is required.